Patent GB-1325673-A (GB)
Title: Reverse osmosis membrane assemblies
IPC: B01D61/10
Filed: 1969-07-16
Abstract: 1325673 Porous pipes and apparatus incorporating them UNITED KINGDOM ATOMIC ENERGY AUTHORITY 8 July 1970 [16 July 1969] 35851/69 Headings F2G and F2P [Also in Division B1] A semi-permeable membrane assembly is produced by winding one or more porous fibrous tapes to form a single or multiply porous tube in which in the only ply, or in at least one ply, the tape forming the ply is overlapped on itself by up to 25% of its width, the or at least one tape which provides such an overlapped ply being heat or solvent sealable to itself, and heat or solvent sealing at least the overlapped portions of one tape, and providing the tube with a semi-permeable membrane as an inner or outer ply during or after winding the tape or tapes. When more than one ply is present each ply may comprise an overlapped tape, each overlapped tape may be heat or solvent sealable to itself, and more than one ply with such a tape may be sealed at the overlap. Where more than two plies are present an intermediate ply may comprise the only sealed tape overlap. Where two or more plies are wound adhesive may be used between the plies, the adhesive being either porous or applied in a pattern. Hot melt powdered thermoplastics (e.g. polyethylene) are suitable adhesives. The or each tape may comprise organic or inorganic fibres and may be woven, air layed, or made as a paper. Preferably the sealable tape or tapes are made from a paper of synthetic fibres (e.g. polyester) and the surface of the tape which forms a surface to which the semipermeable membrane is applied may be treated before or after winding with an agent to render the surface and membrane compatible. The semi-permeable membrane may be applied to the inner surface of the tube by introducing a casting dope into the tube and then passing the tube over a flexibly secured bob at controlled speed. The layer is air dried and excess solvents and modifiers or swelling agents are leached out in a cold water bath before curing in a hot water bath. Alternatively the surface of the tape which forms the inner or outermost surface of the tube may be coated (e.g. by extrusion) with a membrane layer. The membrane material may be cut into strips from a sheet and wound in overlapping relation (with suitable adhesive) to form the inner or outer surface of the tube. Modified cellulose (see Specification 1,056,636) may be used as a membrane material. Membrane assemblies 10 made as described above are incorporated in an apparatus shown in the Fig. Each assembly 10 is supported within a stainless steel tube 11 provided with perforations 12. The steel tubes 11 are inserted in a header 13 at each end and resilient bushes 14 inserted within the membrane assemblies. The flanges 15 of the bushes locate in rebates 20 surrounding ports in the moulded plastics end caps 18 which are held to the headers by screws 19. A casing 16 is located to seal with the headers via rings 17. Each cap 18 includes U- shaped passages joining the ports such that the assemblies are connected in series. As shown fluid may be introduced via a through passage 22 to one of the assemblies and is removed via a similar passage in the other end cap (not shown). Other end caps are described in which both inlet, egress, and U-shaped passages are provided in one cap and only U-shaped passages are provided in the other cap. Square caps may be used and arrangements of the U passages for use with various numbers of assemblies 10 are described. The header 13 and caps 18 may be cast in glass filled epoxy resin. The form and nature of the end caps form the subject matter of Specification 1,325,674. Specifications 1,256,491 and 1,325,672 are referred to.